CW-onderful Part 1: DIY Assembly and Installation Of 500Hz Rockwell Collins Mechanical Filter (526-8693-010) Into Yaesu FT-818nd (A YF-122C clone!)

First off, go to Thomas Witherspoon K4SWL’s blog on this. I stole the idea directly from him. Well from a reader (Petr OK1RP) of the blog that commented that this was possible, and then Thomas documented it.

I have been dipping my toe into CW for a while now. I am a member of the Long Island CW Club, though rather inactive now. I head copy up to 10wpm ARRL code practice MP3s on my walk home from work. I listen to call signs generated through the Morse Trainer android app. I have played a few hours of Morse Machine on my cell phone. I have restored a CW straight key. Heck, even put together a QRPme Rockmite II 40M CW transceiver that I never quite finished. I have even made a few contacts in some contests, like this one. And hunted a rare POTA station…

And by now it should be obvious that I am an avid portable operator. Especially Summits-On-The-Air where I am working to acquire the 1000 points needed to get my Mountain Goat Award. So, being able to bring up a small rig is incredibly appealing. I specifically do not enjoy QRP for SSB. But CW is an entire different story!

One day I brought my Yaesu FT-818nd with me to a park. For those that may not know, this is a 6 watt shack-in-a-box transceiver. The kid sister of the now-discontinued, badass, HF/VHF/UHF all-mode Yaesu FT-857D. My goal was to hunt some CW POTA. To my dismay, when I went looking for a station on the low end of the HF ham bands, I heard a cacophony of dits and dahs…like a CW pile-up of overlapping stations. I went to narrow down the bandwidth, and for the first time, I realized that there was no appropriate filter for CW on this cute little radio. My smallest QRP rig was useless for CW!!! And when I got some time to look for a filter for it, I realized that the FT-818nd 500Hz Collins CW filters were no longer made, and no one was selling any. Yaesu marketed the 500Hz filter as the YF-122C. For the record, and even more narrow 300Hz filter, the YF-122CN, was once available too. These are now pure unobtainium…

A little research though led me to the QRPer blog post showing how to obtain a filter. Let’s just say it has a bit of a back alley, “tell ’em Joe sent ya” feel to it…

First off, you need to track down a filter. I bought mine on Ebay here from the Japanese seller zizai_01. The name of the product is: AOR MF500 500Hz MF Series Collins Mechanical Filter 526-8693-010.

It arrived with some custom artwork and origami instructions.

As well as a pre-folded origami crane! Even the packaging was artistic… I was so touched I bought another one from the same seller for my Yaesu FT-857D.

Next, you need to email some guy in Poland. Seriously, Artur SP6AB [sp6ab@butryn.org]. Let him know what specific filter you bought. He will send you instructions on how to go about buying his custom printed circuit boards for the Yaesu 817/818nd and 857D.

His packaging is equally intriguing, crossing the Atlantic in utilitarian corrugated cardboard and tape within a greeting card envelop.

And a closer look at his boards…

There is not much trick to this. You can see the three posts on the bottom of the Collins filter sticking up. These align with the three holes inside the “Yaesu Filter Board” box on the PCB.

Line them up, and solder them in place. Just remember the surface mount components, already soldered on thanks to Artur, go on the opposite side of the board than the filter.

Now the filter needs to be placed in the transceiver. I remove the protective Portable Zero rails from the radio.

Looks so bare without them, doesn’t it?

I take out the internal battery next, just in case. One screw holds the battery compartment cover down.

There is a small connector attaching the battery to the radio. Simply pull this apart.

It looks like this…

Now time to pop the case open. Three screws hold down the top portion of the cabinet. Two are in the front…

…And one is in the back. The case can be gently pried open at this point.

Just be a bit careful because there are wires that attach from the main board in the body of the radio to the speaker in the lid of the radio. You do not want to pull them apart!

This is a closer look at the main board of the 818nd. It should be obvious where the filter board goes at this point.

If you look closely at the filter insertion site, you can see there are 3 pins on the right side (trust me!) and 4 pins on the left side. This lines up precisely with the filter board.

Simply line up the pins of the main 818nd board with holes on the CW filter and gently push it into place. That’s it! The purple item behind the filter is a sticky cushion used as a stand-off to keep the radio lid in place and off the filter.

Reinsert the battery or just power the transceiver externally like I did. And turn it on. Now find menu option 38 which allows you to chose which optional filter you would like. Choose CW.

Return to the main VFO display and hit the “F” function key quickly. This will bring up the quick key buttons at the bottom that every Yaesu radio fan is highly familiar with. Scroll through these until you reach the “IPO” “ATT” “NAR” group. Select NAR, indicating a narrow filter. That’s it. You are done!

But, how can I test if this filter is working?!

My qth antenna is attached to an Alpha Delta coax switch.

So I attached my SDRPlay to the antenna switch with one coax jumper. And I attached the transceiver to the other output of the antenna switch. Now I could toggle between the SDRPlay and the 818nd.

BY using the SDRPlay Uno software, I was able to locate an area where there was fairly dense CW. Look at the noise level at my qth!! Anyway, I decided 7.036MHz would do the trick. The passband of the native filter in the 818nd is 2.2 kHz wide at -6dB and 4.5 kHz wide at -60dB. This means that normally I would expect to hear multiple cw operators if I tune in at 7.036 MHz without activating the newly added narrow filter. Note that the red line is the center frequency of the SDRPlay, and the grayed area is what 500 Hz CW filter looks like visually.

The YF-122C filter has a passband of 500 Hz at -6dB and 2 kHz at –60 dB. This is identical specs to the filter that I assembled in this blog post. Essentially this should mean I could tune around 7.036 and not be able to hear any CW when the filter was engaged, being in between the 2 closest frequencies of the CW operators.

So I tried it. And sure enough, I could hear multiple operators without the narrow filter on when I tuned to 7.036. However, the morse code disappeared when I switched the filter on. The difference, as I tuned around the band some more, was very noticeable when the narrow filter was engaged versus when it wasn’t. I am very pleased with the results!

I secured the lid of the radio back into place. I reinserted the internal battery. And I put the rails back on. Now, if only I could actually do CW… (But that story is for Part 2 of CW-onderful!)

Always Yours,

KM1NDY